It is well known that the incidence of dental diseases has been different in different periods of development of humanity and that lately it has increased substantially. The increase is due to the altered lifestyle of modern humans, especially in relation to the economic well-being and comfort. The better the economic status of the society, the higher the morbidity due to dental diseases. This trend is also observed in animals. Mostly, wild animals are immune to dental conditions. The high morbidity is found in domestic animals and, in particular, in pets.
Thus, a complete analogy of the pathogenic effect of the “humanised” conditions of development of animals, ancient humans and contemporary people on the dento-alveolar system was revealed.
Keywords: dental conditions, domestication, self-domestication, acid resistance of the enamel.
The signs of the phenomenon in question have been observed for a long time by humans. It has been known for a long time that the current mass prevalence of dental disease is not a species-specific trait, but a characteristic acquired by humans. Since 1772, the French physician D. De La Salle published a study presenting data from excavations in an old multi-level cemetery. The researcher described a striking correlation between the condition of the teeth and the depth at which the remains were found. The deeper and consequently the older the remains, the healthier the teeth. All subsequent studies have confirmed that dental diseases have indeed been tied to the course of history of humankind in quite an unexpected way. The more economically developed a society was, the better its living conditions and the longer people lived, and yet, the healthier they were, the condition of their teeth was getting worse! It is a rather unfortunate fact: today, in economically prosperous regions, half of children’s teeth have growth abnormalities, and in more than half of the adults their teeth become mobile and are lost due to periodontitis. Almost all tooth crowns are affected by caries. The “Europeanisation” of the planet has turned this ridiculous situation into a global phenomenon.
The De La Salle phenomenon (let us call it that way), invariably confirmed in thousands of archaeological discoveries, has long since lost any intrinsic scientific value, becoming, in two hundred years since its discovery, an uninteresting, ordinary fact. It has become obvious: the course of history has undoubtedly changed the qualities of food. It has become increasingly “harmful” locally, softer and most importantly, sweet, being harmful to teeth and gums, overflowing with refined flour and sugar – “the tooth’s sworn enemies”, a well-known fact.
However, a small, but important, digression is required here in terms of “well known” pattern. In fact, for many scientists around the world, this has always been very controversial, unproven and recently questionable. “Evidence-based medicine” could not confirm the validity of this almost universally recognized position, and data on the epidemiology of caries have made it uncertain. Thus, the expected decrease in prevalence in millions of diabetics, forced to follow even the most severe sugar-free diet, ran contrary to the point of view of these “generally recognised” local ideas. On the contrary, it has proved impossible to somehow correlate the unexpected spontaneous improvement in the dental health of millions of children in the West with a decrease in the consumption of sweets and with oral hygiene. This improvement has been achieved through the spread of fluorides, their mechanism of action and their overall benefits, which causes serious concerns. Consequently, the “victory” over caries, attributed in the USA to the most important achievements of twentieth century science, thus proves to be an ordinary fiction. As for tooth decay, as well as periodontitis and malocclusion, their triumphal procession on the Europeanised planet has in fact remained a mystery, an unpleasant companion to the scientific and technological progress.
The situation described above determined Acad. A.I. Evdokimov – one of the founders of Soviet dentistry – to attempt to reiterate the analysis of the underlying causes of mass injuries of the oro-facial system among modern, civilised people, suggesting it to the author of these very lines as the subject of a PhD thesis .
The literature and our personal materials (more than a thousand skulls) allowed us to clarify the pattern described by De La Salle. The historical aspect was shown to be related not so much to the passage of time itself, but rather to the evolution of the common household, to the economic status of a certain population. The higher the economic status was, the worse the condition of the teeth. At the same time, the greatest difference in the incidence of caries was between the nomadic tribes and their sedentary contemporaries, which was particularly obvious in children. Attention was drawn to the fact that all this happened thousands of years (!) before the invention of refined sugar and flour. (The generally accepted position on the fatal role of easily digestible carbohydrates has thus been revised.)
This conclusion also emerged from a later discovery. Thus, it was found that the three groups of diseases, undoubtedly different, which concern modern dentistry, are in fact a single complex of pathologies, whose prevalence varies from population to population almost in a parallel line. The triad of the aforementioned dento-alveolar afflictions (cavities, periodontitis, malocclusion) is closely related: no known populations prone to one pathology and immune to the other two were detected (fig. 1). The presence of malocclusion in this triad (i.e. distinct developmental defects) directly indicates the probable cause of the parallelism in the prevalence of these pathologies (i.e. some specific characteristics and the deficiency in the development of the dento-maxillary apparatus).
Thus, paleontological materials revealed that the “package” of dental diseases in the past was associated with the level of development of the population. The “inhuman” life conditions (and the subsequent development) have proven to be the desired protective condition that determines the low incidence of dental diseases in the past eras. To what extent this pattern applies to modern humans and the animal kingdom has been clarified in a number of subsequent studies.
When studying the dental health of modern people (in the 1960s) among the recently nomadic Romani children and the European townspeople, the researchers found a striking difference in the affliction with caries: the Romani children, just like the similarly aged ancient nomadic children, were almost immune to tooth decay. A similar result was yielded by the study of the dental health of four hundred army recruits. The main group was divided into subgroups according to the level of tooth decay. As it turned out, the prevalence level corresponded to their economic status. We attributed unfavourable economic conditions to: a large family, rural residence, child labour and the semi-nomadic life of their parents. As it turned out, these family circumstances of the selected subjects determined, at the same time, their relatively low stature and a significantly higher resistance to caries. Paleopathology data have thus been supported by contemporary studies.
The harmful effect of living with modern humans on the condition of the masticatory apparatus in animals can be attested by veterinarians, who have long observed the precarious condition of the teeth in domestic animals and especially in pets. Moreover, the study also inspected many hundreds of objects from the museum’s collections, concluding that even synanthropisation (living in the close proximity of humans, for example in an auxiliary building) leads to a significant increase in “spontaneous” periodontitis, practically absent in the unconditionally wild non-synanthropic specimens (Fig. 2.). Thus, a complete analogy of the pathogenic effect on the dento-alveolar system inflicted by the modified “humanised” conditions for the development of animals, ancient and modern humans was revealed.
Already in the middle of the last century, due to the aforementioned works, it has become obvious that the traditional search for unfavourable factors that cause a dramatic local pathogenic status is, in principle, unpromising. Not harmful environmental conditions, but on the contrary – the welfare, the soft foods determine the increased prevalence of dental diseases. Consequently, not some optimal, well-balanced conditions, but on the contrary, the harshness of the living conditions favourably influence the development of teeth. A complex “tooth weakness” is a clear consequence of changes in individual development (ontogenesis).
As a result, the problem of the mass prevalence of dental pathology has emerged as a particular manifestation of “general issues of change in human physical development”. This position subsequently prompted a further search for the causes of the dental pandemic in order to completely abandon the generally accepted local hygiene viewpoint in favour of a systemic, biological one .
Such a strategy proved fruitful and, in a relatively short time, a previously unknown phenomenon was discovered: the “biomechanism of active protection of the tooth integument”, determined by the general condition of the body. We are talking about the centrifugal movement (the “flow”) of the interstitial fluid of the tooth that protects the internal environment of the micropores of its integument from the penetration of the chemical and microbial agents of the oral cavity. This previously unknown biological phenomenon seems to be universal and works perfectly in all mammals. There is a clinical test based on it (Enamel Resistance Test – ERT), which reveals the extent of its activity, allowing the prediction of the caries occurrence. It has been used for this purpose for several decades in different projects about caries research and prevention. At the same time, the very existence and the content of this discovery and its obvious implications for our specialty continue to remain in a deep shadow.
Something similar happened in another field of research – in fundamental biology. In 1970, D.K Belyaev made a Darwinist-level discovery, the “destabilising selection phenomenon”. This event, despite its significance (or maybe because of it?) had gone completely unnoticed, just like the previous one, although its practical part continues to exist. Belyaev’s methodology also lives on, but as always, it is more “beyond the hill”. In 2017, at the University of Chicago, based on his own work, the book of his successors L. Trut and L. Dugatkin  was published, which has since been re-edited.
However, the important fact here is not so much the synchronism and the well-known drama of the fate of the two discoveries – the smaller, dental one, and the larger, the general biological one – but their deeply significant similarity.
First of all – we talk about destabilising selection. During evolution, through the implementation and interaction of various types of selection, situations arise when the genotypic parameters of an animal prove to be inadequate to the sudden change of the environmental conditions. The most specialised organisms, which have strictly followed the genetic developmental program, are in a significantly less favourable position. The advantage goes to their opposites, in which the implementation of phenotypes is less stable and allows a much greater freedom of modification (reaction rate), allowing them to adapt to the new conditions. The inexorable selection is on their side.
Conservation of the species requires destabilisation: greater individual variability and plasticity of ontogenesis in all its stages. Under natural conditions, such a gradual pause not only saves the population genetic background, but also offers new means for progressive evolution.
In its most pronounced form, destabilising (or “centrifugal”) selection manifests itself in the domestication of animals. In an immense experiment of domesticating foxes, this previously unknown phenomenon was discovered.
It should be mentioned that the domestication of animals, being a well-known and undoubted phenomenon, has not received in-depth explanations in some respects. It even surprised Charles Darwin, by the fact that many homologous signs, including those that obviously had no adaptive value, were common to various types of pets. We are talking about changes in the morphogenetic plan related to dozens of parameters: from the appearance of the animal to chemical indicators. In addition to the acquired complacency, the hairline was changed in animals, the size of the skull and the brain, of the jaws and teeth decreased, even the usual position of the tail and ears that characterised the appearance of animals has changed. The reproductive function intensified, the life expectancy and the tendency to overeat have increased. These are due to the altered levels of stress hormones in the blood, leading to changes in bone micromorphology and the juvenilisation of many signs (neoteny).
Interestingly, in the study of D.K. Belyaev, selection based on a single behavioural trait of non-aggressiveness involved the emergence of an entire set of specific manifestations, which were later called elements of the domestication syndrome. Today, this concept can be considered universally recognised and, most importantly, related to all domesticated and self-domesticated animals, including, as many believe, humans themselves.
The common biological fate of domesticated species is determined primarily by the general nature of habitat change – food security and safety, which leads to decreased physical activity. People, along with the animals domesticated by them, become more graceful, the size of the skull and jaws decreased, and hair growth changed. They acquired significantly longer lives, with an extended period of reproduction, a tendency to overeat and to hypersexuality, as well as to games that mimic competitive fights and domination.
The list of known common characteristics of domestication should include the precarious state of teeth (the triad mentioned above), which manifests itself mainly in humans in the last century, due to the secular tendency – the flash of juvenilisation (acceleration of puberty).
Regarding the depth of the underlying mechanisms of the general biological phenomenon analyzed, the most probable interpretation identifies a defect in the embryonic development of the neural tube crest, from which derive the skull bones and by the movement of the stem cells that ensure the development of adrenal glands, external integument and teeth. Moreover, there is a connection between the development of this crest and specific mental disorders (autism and schizophrenia) and with phenotypes of “non-domestication” and “over-domestication”. We are interested to include the “dental problem” into the studied phenomenon. The corresponding facts, as mentioned before, are known to humankind since the end of the eighteenth century. However, judging from the available literature, the causal relationship between these phenomena, which are both significant, has not yet been identified and recognised, and these very lines might represent the first attempt of its kind.
Thus, today we have facts that uniquely characterise the situation with our self-domestication. The reality of this phenomenon cannot raise any doubts, as well as the sad lack of interest from the medical and non-medical public, who are mainly interested in the technological and engineering aspects of science. Of course, the morphogenetic and modification variability of our species can be ignored for now, but not cancelled. What we call self-domestication is a kind of universal biological background (or rather, a gravitational field) that affects every step we take on the uncertain path to our biological future. Without at least a general understanding of what nature does to us, any of our decisions might prove fatal or at best simply inadequate. So far, most often, we faintly realise only in the depth of our consciousness the fact of our current instability and fundamental biological transformations, but we are not too interested in them. We accept the world and our place in it as we have found it, we do not celebrate the birthday of the species, we do not honour our prehistoric ancestors and most importantly, we do not understand whether we are adults or babies. We named what happened and obviously continues to happen –”socialisation”, implicitly assuming that this is related to “knowing the good from the bad”. Nevertheless, we do not take into account the fact that this phenomenon must be based on certain imperceptible, but all-powerful biological processes, those that have changed (and continue to change) our biological essence and that so far we attribute to the formation process of the species Homo sapiens.
This general conclusion is very significant from the point of view of approaching the understanding of the role of domestication in our past and future. However, the solution to the private dental problems is only a confirmation and concretisation of the ideas formed in the 1960s: the root of the three dental problems must be sought in the biological mechanisms of the decline of resistance that came to us from the depths of phylogenesis.
Our “Europeanised” contemporaries and their ancestors are healthy in different ways. Some of them – because of security (especially medical one), others – on the contrary – because of the harshness that gave them natural resistance. The dental pandemic characteristic of the former is a marker of their biological instability, which is typical, in one way or another, of all domesticated animals. Therefore, a more complete description of us, modern “dental professionals”, would have to add “but not for our teeth”, regardless of the technological peaks we have reached. It can be solved, but only through the joint efforts of anthropologists and physicians who have realised the fundamental importance of our continuous biological formation.
Of course, the mechanical effect on the elements of the pathology (carious cavity, periodontal pouch, dental dystopia), which dentists have always been concerned with, is eternal and inevitable, but will be significantly complemented by biomedical approaches. Today it is premature to talk about the specific organisational techniques, diagnosis, therapeutic and preventive measures that will be applied by our colleagues from the next generations. At the same time, the outline of the general, personalised preventive approach is already quite clear. It will be necessary to identify and diagnose a special condition of the body, which until now does not even have a name, connected to the concept of pre-illness (“precarious”). Today we know that these conditions occur spontaneously, mainly in individuals with an appropriate predisposition, i.e. we should assume that they have a pronounced manifestation of the domestication syndrome. We know that these conditions, even preliminarily, can be determined clinically by attesting a decrease in the acid resistance of the tooth’s enamel detected through ERT sample. We also know that this clinical manifestation reflects the real characteristics of interstitial fluid flow of the tooth and obviously of the whole body. We know that this condition is, in principle, medically corrigible, especially by means that increase the non-specific resistance of the body (neuro-mediators, eleutherococcus, ascorbic acid, etc.). Indeed, we have understood for a long time the local mechanisms of the microbial destruction of hard tissues of the tooth and the periodontal ligament – the foci of the clinical manifestations of these diseases. The rest is unknown to us and will remain so for the time being, as many specialists are still convinced of the local-hygienic nature of the corresponding pathology. The facts outlined above and the presented arguments should expedite to some degree the process of convincing our esteemed colleagues to initiate the appropriate reorientation of our specialty. The first step in this direction will be a public awareness of an obvious circumstance, although not a very pleasant one.
We humans are a domesticated biological species, with all the inherent consequences of this phenomenon; we cannot fundamentally negate it (at least until the genome reconstruction era). At the same time, in order to alleviate its dangerous and simply unwanted problems, such as dental manifestations, we are capable together to do it.
However, the Word was always in the beginning and we hope that these lines will serve to formulate it, at least to some extent.
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2. Okushko V, Zagnat V. Aspecte de fiziologie a dintelui. Tipografia T-Par, Chișinău, 2018.- 122 p. (Okushko V, Zagnat V. Aspects of tooth physiology. Tipografia T-Par. Chișinău, 2018.- 124 p.)
3. Dugatkin L, Trut l. How to tame a fox. University of Chicago Press, 2017.